Tool holder

ABSTRACT

A tool holder has a cutter arbor. The cutter arbor has a shank portion detachably mounted on a spindle, and a mechanism for holding a cutting tool. In the cutter arbor portion, a cavity portion is formed. In the cavity portion, a vibration damping material is filled at a filling rate so as to be capable of obtaining predetermined vibration damping characteristics. Thus, it is possible to provide high vibration damping characteristics, effectively damp vibrations during cutting and improve working precision, without using any special materials, such as damping materials, although the tool holder has a usual shape.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a tool holder forattaching a cutting tool to a spindle of a machine tool.

[0003] 2. Description of Related Art

[0004] In machine tools, a cutting tool is exposed continuously tocutting resistance forces and so forth during a cutting process for awork piece, so that vibratory forces are unavoidably generated. Sincevibrations generated in the cutting tool have a harmful influence onworking precision in machine tools, so that various measures areconventionally taken.

[0005] In general, the cutting tools and tool holders are made ofmaterials having high vibration damping characteristics to inhibitvibrations during cutting processes, and/or tool holders are integrallyformed with damping materials by welding or shrinkage fit to inhibitvibrations.

[0006] In addition to the enhancement of the vibration dampingcharacteristics of the tool holder itself, it is a well-known art toincorporate a damping mechanism in a spindle unit. For example, JapanesePatent Laid-Open No. 1994-277806 discloses a damping mechanism in whichelastic body and a viscous fluid are filled between a spindle unit and aspindle head to damp vibrations by the elastic deformation of theelastic body and the viscous resistance of the fluid.

[0007] However, it is not possible to expect effective damping capacityby depending on the vibration damping characteristics of the materialsthemselves of the tools and tool holders like conventional measures. Inparticular, vibrations are transferred to a machined surface infinishing machining, so that the working precision on the machinedsurface deteriorates. In addition, the damping materials have a problemin production costs since the damping materials are generally expensive.Moreover, there is a problem in that it is not obtain a damping actioneffective in the prevention of fretting which is caused on the innerperipheral surface of a tapered hole of a spindle contacting a tapershank of the tool holder.

SUMMARY OF THE INVENTION

[0008] It is therefore an object of the present invention to eliminatethe aforementioned problems and to provide a tool holder which has highvibration damping characteristics, which can effectively damp vibrationsduring cutting processes and which is effective in the improvement ofworking precision, without using any special materials, such as dampingmaterials, although the tool holder has a usual shape.

[0009] In order to accomplish the aforementioned and other objects,according to one aspect of the present invention, a tool holder for aspindle of a machine tool, said tool holder comprises an arbor having ashank portion which is detachably attached on the front end of thespindle, and a mechanism for holding a cutting tool, a cavity portiondefined in the arbor; and a vibration damping material charged in thecavity portion at a predetermined charging rate in a manner that thedamping material shows vibration damping characteristics.

[0010] According to the present invention, by vibrations produced duringa cutting work, sand particles filled in the cavity portion collide witheach other and with the walls of the cavity portion to convertvibrational energy into thermal energy, so that vibrations can graduallyattenuate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will be understood more fully from thedetailed description given herebelow and from the accompanying drawingsof the preferred embodiments of the invention. However, the drawings arenot intended to imply limitation of the invention to a specificembodiment, but are for explanation and understanding only.

[0012] In the drawings:

[0013]FIG. 1 is a partially sectional side view of a preferredembodiment of a tool holder according to the present invention; and

[0014]FIG. 2 is a sectional view taken along line A-A of FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

[0015] Referring now to the accompanying drawings, a preferredembodiment of a tool holder according to the present invention will bedescribed below.

[0016]FIG. 1 shows a tool holder in this preferred embodiment. Referencenumber 2 denotes an arbor constituting a body of a tool holder. On thefront end portion of the arbor 2, a tool mounting portion 4 is provided.A cutting tool 6 is attached into the tool mounting portion 4 to befixed thereto by means of a bolt (not shown).

[0017] The arbor 2 has a shank portion 7 and a flange portion 8. On theend portion of the shank portion 7, a pull stud 9 is fixed. By insertingthe shank portion 7 into a tapered hole open on a spindle and bygripping and pulling the pull stud 9 by means of a collet connected to adraw bar built in a spindle, the arbor 2 can be fixed to the spindle.

[0018] As shown in FIG. 2, a ring-shaped groove is formed in the endface of the flange portion 8 of the arbor 2. By sealing the ring-shapedgroove with a cover member 10, an annular cavity portion 12 filled witha vibration damping material therein is defined coaxially with the arbor2. This cavity portion 12 is preferably arranged nearer to the cuttingtool 6.

[0019] In this preferred embodiment, the vibration damping material is aviscous fluid, such as an oil, in which sand is densely mixed so thatsand particles contact each other.

[0020] As the vibration damping material, only fine sand densely chargedmay be applicable. In addition to sand, fine glass particles, ceramicfine particles and metal particles may be used. The particle size andshape of the particles are not uniform but preferably uneven.

[0021] With this construction, the operation of the tool holder in thispreferred embodiment will be described below.

[0022] When a cutting work is carried out, if the spindle is moved whilerotating, the cutting tool 6 mounted on the tool holder cuts a workpiece. In the cutting process, vibratory forces are generated by cuttingresistance forces and so forth, and transferred from the cutting tool 6to the arbor 2 to vibrate the arbor 2. By the vibrations, the sandparticles charged in the cavity portion 12 start to move to collide witheach other and with the walls of the cavity portion 12. Thus, vibratoryenergy is converted into thermal energy, so that the vibrationsgradually attenuate. Therefore, in the finish machining, it is possibleto prevent vibrations from being transferred to the machined surface.Since the movement of the particles is converted into thermal energy, itis possible to obtain a larger damping action than conventional toolholders which use special damping materials. In addition, by adjustingthe charging rate and grain size of the particles, it is possible toobtain damping characteristics which are effective in the prevention offretting wear caused on the outer peripheral surface of the shankportion 7.

[0023] By thus charging particles, such as particles of sand, in thecavity portion 12 in the arbor 2, it is possible to provide dampingcharacteristics, which are not possessed by usual tool holders, to thetool holder to damp vibrations during the cutting work.

[0024] Furthermore, a viscous fluid may be charged at a flowablecharging rate without using particles. In this case, vibratory energy ischanged to thermal energy by the shear of the fluid according to themovement of the fluid, so that vibrations can be damped. Although thewhole tool holder is unbalanced so that the center of gravity isslightly shifted from the shaft center, the fluid in the cavity portion12 automatically compensates the unbalance of the tool holder inaccordance with the rotation of the tool holder during working.

[0025] As described above, according to the present invention, a toolholder comprises a cutter arbor having a shank portion which isdetachably mounted on a spindle, and a mechanism for holding a cuttingtool, wherein a cavity portion is formed in the arbor, and a vibrationdamping material is filled in the cavity portion at a filling rate so asto be capable of obtaining predetermined vibration dampingcharacteristics. Therefore, it is possible to provide high vibrationdamping characteristics, effectively damp vibrations during cutting andimprove working precision, without using any special materials, such asdamping materials, although the tool holder has a usual shape.

[0026] While the present invention has been disclosed in terms of thepreferred embodiment in order to facilitate better understandingthereof, it should be appreciated that the invention can be embodied invarious ways without departing from the principle of the invention.Therefore, the invention should be understood to include all possibleembodiments and modification to the shown embodiments which can beembodied without departing from the principle of the invention as setforth in the appended claims.

What is claimed is:
 1. A tool holder for a spindle of a machine tool,said tool holder comprising: an arbor having a shank portion which isdetachably attached on the front end of the spindle, and a mechanism forholding a cutting tool, a cavity portion defined in the arbor; and avibration damping material charged in the cavity portion at apredetermined charging rate in a manner that the damping material showsvibration damping characteristics.
 2. A tool holder according to claim1, wherein said vibration damping material comprises particles of a hardmaterial, or a mixture of particles and liquid.
 3. A tool holderaccording to claim 1, wherein said vibration damping material is aviscous fluid which is filled at a flowable charging rate.
 4. A toolholder according to claim 2, wherein said hard material comprises sandsor fine particles of glass, metal, or ceramics which lacks in uniformityof size and shape.
 5. A tool holder according to claim 1, wherein saidcavity portion is defined between a cover member and a flange portion ofthe arbor.
 6. A tool holder according to claim 1, wherein said cavityportion has a generally annular cross section coaxial with the arbor.